1. Field of the Invention
The present invention relates to the manufacture of apparatus used in the injection molding and extrusion of plastic and, more particularly, a feed screw for use in such processes, the feed screw having a wear resistant alloy coating thereon.
2. Description of the Related Art
Feed screws are used in combination with injection molding cylinders and extrusion barrels to process plastics. The feed screws are used to convey, melt, pressurize and pump plastic resins. The screws usually include a coating of a wear resistant alloy on the wear surfaces of the screw, and the barrels and cylinders usually also include a coating of a wear resistant alloy, known as inlay, on the inner surfaces of the barrel or cylinder. Such screws, known as bimetallic screws, have been manufactured by conventional processes, such as detonation cladding.
However, conventional bimetallic screws have a limited lifetime (usually on the order of twelve months) and it has been difficult to apply a nickel-based wear resistant alloy coating to steel feed screws.